The present invention relates to braided structures and braiding techniques in general and, more particularly, to braided reinforcement of generally tubular structures.
Tubular composite parts that are repeatedly subjected to moderate to high stress and/or pressure levels, for example, fuel tanks, jet engine parts and airplane fuselages, must be structurally reinforced to provide reliable, safe operation at all design load conditions. Typically, such parts are constructed from a number of elements or subassemblies which are reinforced at various locations using reinforcement members that are typically attached to the parts using adhesive bonding or mechanical fasteners such as rivets or bolts. This reinforcement method is generally reliable; however, the reinforcement members and attachment means add undesired weight to the reinforced parts and increase production costs. This problem is particularly significant in airplane parts, where weight, cost and safety are critical considerations for design and manufacture.
Braid-reinforced structures of various shapes and forms are known in the art. For example, braid-reinforced tubular structures are used in the composites industry for recreational equipment, e.g., snow boards, baseball bats and tennis rackets. Braid-reinforced tubular structures are also used in prosthetic devices, aerospace parts, e.g., vanes and bushings, and other products requiring a relatively strong, light weight construction, for example, light poles. Such tubular structures are typically formed by mounting pre-braided sleevings over mandrels having the desired shapes of the finished products. The braided structure is placed in a tool or die cavity and resin is introduced into the braid using well known methods, such as resin transfer, gravity feeding or resin film infusion. Finally the parts are consolidated and/or cured, in a heated mold, oven or autoclave, typically under vacuum or pressure conditions.
It is an object of the present invention to provide a braid-reinforced, generally tubular, structure for use in generally tubular parts, particularly parts designed to endure medium to high stress and/or pressure levels, for example, pressurized vessels and airplane parts such as fuel tanks, jet engine parts and fuselage.
It is another object of the present invention to provide a method of manufacturing a braid-reinforced, generally tubular, structure.
It is yet another object of the present invention to provide a braid-reinforced, generally tubular, structure having a predefined configuration of indentations thereon.
In accordance with an embodiment of the present invention, there is provided a method of producing a braid-reinforced, generally tubular structure, the structure including an inner layer having a predefined indentation configuration, the method including:
providing a mandrel having a shape and configuration of indentations corresponding to the shape and indentation configuration of said inner layer;
providing a plurality of support members along at least some of the indentations of said mandrel, the support members protruding a predetermined distance radially outwards from the surface of the mandrel;
forming an inner layer braid surrounding the mandrel and the support members thereon; and
removing the support members from their protruding positions along at least some of the indentations.
To remove the support members from the vicinity of the indentations, the support members may be detached from the mandrel or retracted into a non-protruding position, e.g., into the interior of the mandrel.
In some embodiments of the present invention, the method further includes the step of over-braiding the inner layer of the generally tubular structure with at least one additional braided layer, thereby to provide further reinforcement. Additionally, preformed reinforcement or stiffener members may be installed on the inner layer, along the locations of the indentations on the mandrel, before the inner layer is overbraided with the at least one outer layer. The preformed reinforcement or stiffener members may be pre-shaped to conform to the shape of the indentations in the surface of the mandrel, so as to force the inner layer into contact with the surface of the mandrel within the indentations.
The use of the support members in forming the braided structure results in a braid which is larger in diameter than the mandrel in the vicinity of the indentations. Once the inner layer braid is pushed into the indentations of the mandrel, e.g., by the preformed reinforcement members and over-braiding described above, the excess amount of braided material in the vicinity of the indentations enables the inner layer to adapt to the shape of the indentations in the surface of the mandrel. By controlling the dimensions of the support members and/or the reinforcement members, the inner layer of the braided structure can be adapted to fit the shape of the mandrel with a desired degree of stretching.
In a preferred embodiment of the present invention, the method further includes the step of curing the braid-reinforced, generally tubular structure to provide added reinforcement and rigidity to the structure.
In accordance with an embodiment of the present invention, there is also provided a braid-reinforced, generally tubular structure including an inner braided layer having a predefined configuration of indentations. The braid-reinforced tubular structure may further include at least one outer braided layer. In some embodiments, the braid-reinforced, generally tubular structure includes a plurality of reinforcement or stiffener members disposed in the spaces defined between the outer layer and the inner layer. The reinforcement or stiffener members may include axial and/or circumferential reinforcement members and/or reinforcement members at any other predefined angle.
In one embodiment of the invention, the generally tubular object includes at least a portion of a pressurized vessel, such as a fuel tank. In another embodiment of the invention, the generally tubular object includes at least a portion of a fuselage. In yet another embodiment of the invention, the generally tubular object includes at least a portion of a jet engine part, for example an exhaust shroud or a duct.